Radio-Frequency Identification (RFID) technology has become widely used in virtually every industry, including transportation, manufacturing, waste management, postal tracking, airline baggage reconciliation, and highway toll management. One common use of RFID technology is in an Electronic Article Surveillance (EAS) system that is to protect against shoplifting or otherwise unauthorized removal of an article. In particular, an EAS system may be used to detect the presence of EAS markers (tags) that pass through an energizing field. Retail outlets, libraries, video stores and the like make use of RFID technology in conjunction with EAS systems to assist in asset management, organization, and tracking of inventory.
A typical RFID system includes RFID tags, an RFID reader, and a computing device. The RFID reader includes a transmitter that may provide energy or information to the tags, and a receiver to receive identity and other information from the tags. The computing device processes the information obtained by the RFID reader. In general, the information received from the tags is specific to the particular application, but often provides identification for an item to which the tag is fixed, which may be a manufactured item, a vehicle, an animal or individual, or virtually any other tangible article. Additional data may also be provided for the article. The tag may be used during a manufacturing process, for example, to indicate a paint color of an automobile chassis during manufacturing or other useful information.
The transmitter outputs RF signals that create an energizing field, from which the tags receive power, allowing the tags to return an RF signal carrying the information. The tags communicate using a pre-defined protocol, allowing the RFID reader to receive information from multiple tags in parallel, or essentially simultaneously. The computing device serves as an information management system by receiving the information from the RFID reader, and performing some action, such as updating a database or sounding an alarm. In addition, the computing device serves as a mechanism for programming data into the tags via the transmitter.
To transfer data, the transmitter and the tags modulate a carrier wave according to various modulation techniques, including amplitude modulation (AM), phase modulation (PM), frequency modulation (FM), frequency shift keying (FSK), pulse position modulation (PPM), pulse duration modulation (PDM) and continuous wave (CW) modulation. In particular, the transmitter makes use of an amplifier, typically a Class-A or a Class-A/B amplifier, to drive an antenna with a modulated output signal. These amplifiers may require significant power to communicate with the tags. An amplifier may require, for example, 10 watts of power to produce an RF signal having a single watt of power. In other words, a conventional reader may dissipate over 9 watts of power to produce a single watt of output, resulting in approximately 10% efficiency. The heat dissipation requirements and power consumption of such an amplifier are not well suited for a number of applications, including those that require a low-cost, hand-held RF reader. Consequently, conventional hand-held readers may have smaller power outputs, such as 100 milliwatts, but have limited communication ranges and similar power inefficiencies.